The present invention relates to a method for producing a 2,2-dimethyl-3-(1-propenyl)cyclopropanecarboxylate ester useful as an intermediate for preparing pyrethroid compounds which are active ingredients in insecticide or acaricides.
Prior, it has been known that certain ester compounds in which their acid part is 2,2-dimethyl-3-(1-propenyl)cyclopropanecarboxylic acid exhibit an excellent insecticidal effect in Japanese examined patent publication Nos. sho-54-3062B and sho-50-6629B. A method for producing 2,2-dimethyl-3-(1-propenyl)cyclopropanecarboxylate ester by Wittig reaction is known in J. Chem. Soc. (C), page 1076 (1970). The Wittig reaction is shown in the reaction formula below. 
According to the description in the above-mentioned reference, work-up procedure needs an industrially disadvantageous several steps including filtration for isolating the objective 2,2-dimethyl-3-(1-propenyl) cyclopropanecarboxylate ester from the reaction mixture.
The present invention gives a beneficial method for producing 2,2-dimethyl-3-(1-propenyl)cyclopropanecarboxylate ester.
The present invention is a method for producing an ester compound given by formula (I): 
wherein R1 represents a C1-6 alkyl group, C3-6 cycloalkyl group, C2-6 alkenyl group or C4-6 cycloalkenyl group,
which comprises allowing to react an aldehyde compound given by formula (II) 
wherein R1 has the same meaning above,
with a phosphorane compound given by formula (III): 
wherein R2 represents a hydrogen atom, halogen atom or C1-4 alkyl group, in an organic solvent, and obtaining a liquid distillate by heating the above reaction product with water.
The present method gives the ester compound given by formula (I) in high yield and by an industrially available procedure.
The present method is explained in detail below.
The present method generally contains two steps, namely a step for allowing to react an aldehyde compound given by formula (II) with a phosphorane compound given by formula (III) in an organic solvent to give a reaction product and another step for obtaining a liquid distillate by heating the reaction product obtained in the first step with water.
At first, the first step is explained below.
The first step is a reaction of an aldehyde compound given by formula (II) with a phosphorane compound given by formula (III) in an organic solvent and the phosphorane compound utilized in the first step can be prepared in the reaction system.
The organic solvent used in the first step is an inert solvent in Wittig reaction. Examples of such organic solvent include tetrahydrofuran, N,N-dimethylformamide, methyl t-butyl ether, ethylene glycol dimethyl ether, toluene, hexane, heptane and mixtures thereof.
The phosphorane compound can be prepared by a reaction of a phosphonium salt compound given by formula (IV): 
wherein X represents a chlorine atom or bromine atom and R2 has the same meaning above, with a base. Examples of the utilized base include powdery sodium methoxide, potassium t-butoxide, potassium carbonate, sodium hydroxide and potassium hydroxide. The used amount of the base is usually 0.9 to 1.5 mols, preferably 1.0 to 1.3 mols, based on 1 mol of the phosphonium salt compound. The temperature for preparing the phosphorane compound is usually in the range of xe2x88x9220 to 120xc2x0 C.
The phosphorane compound is used at a rate of 0.9 to 2.0 mols, preferably 1.0 to 1.2 mols, based on 1 mol of the aldehyde compound. In case that the phosphorane compound is prepared from the phosphonium salt compound, the phosphonium salt compound is used at a rate of 0.9 to 2.0 mols based on 1 mol of the aldehyde compound.
The reaction temperature of the first step is in the range of xe2x88x9220xc2x0 C. to 120xc2x0 C., preferably xe2x88x9210xc2x0 C. and 30xc2x0 C.
The reaction mixture obtained by the reaction of the aldehyde compound with the phosphorane compound can be provided to the second step as it is, though it may be subjected to neutralization by adding acidic water, such as diluted hydrochloric acid, diluted sulfuric acid and so on, to the reaction mixture for the sake of removing an excess of the base used in the preparation of the phosphorane compound.
Next, the second step is explained below.
The second step is a step for obtaining a liquid distillate containing the ester compound given by formula (I) by heating the reaction product obtained in the first step with water.
The amount of water utilized in the second step is usually one to 20 times parts by weight, preferably 5 to 10 times parts by weight based on one part by weight of the aldehyde compound used in the first step.
The method for heating the reaction product obtained in the first step with water is exemplified by a method for heating the total amount of the reaction product obtained in the first step with water in a vessel, a method for heating water in a vessel while adding gradually the reaction product obtained in the first step to the water, a method for heating the reaction product obtained in the first step in a vessel while adding water or blowing steam gradually to the reaction product and so on. These methods are usually carried out under atmospheric pressure and may be carried out under reduced pressure of 26.7 kPa (200 mmHg) or more.
The liquid distillate containing the ester compound given by formula (I) may also contain an organic solvent used in the first step and water. The water can be removed by phase separation and the separated water may be returned to the heating vessel. Concentration of the separated organic layer gives the ester compound given by formula (I) in high purity. The concentration can be performed by evaporation of the organic solvent under reduced pressure.
Further, by-products in the first step remain in the heating vessel of the second step. Though the by-products are precipitated, an adjustment of the amount of water in the vessel can make the precipitated slurry be undisturbed for stirring. The slurry gives phosphine oxide compound which can be recycled for preparing the corresponding phosphine compound, which is easily converted to the phosphonium salt compound given by formula (IV). The conversion of the phosphine oxide compound to the phosphine compound can be performed according to the method described in Chem. Lett., vol.10, pp.1491-1492 (1985).
As described above, the present invention makes it easy to separate the troublesome phosphine oxide compound off.
The aldehyde compound given by formula (II) can be prepared according to the production methods described in Japanese unexamined patent publication No. Hei2-225442A or Bull. Chem. Soc. Jpn., vol.60, pp.4385-4394 (1987). Further, the phosphonium salt compound given by formula (IV) can be prepared according to the description in Ann. Chem., vol.606, pp.1-23 (1957).
Examples of the alkyl group represented by R1 include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, t-butyl group, pentyl group, hexyl group, 2-methylpentyl group and 2,3-dimethylbutyl group, and examples of the cycloalkyl group represented by R1 include cyclopropyl group, cyclopentyl group and cyclohexyl group. Example of the alkenyl group represented by R1 include 2-propenyl group, 3-butenyl group and 2-butenyl group, and examples of cycloalkenyl group represented by R1 include cyclopentenyl group and cyclohexenyl group.
Examples of the alkyl group represented by R2 include methyl group substituted at 3-position of phenyl group and chlorine atom substituted at 4-position of phenyl group.